The incidence of tick-borne encephalitis varies widely in different geographic regions due to local difference in the rate of infected vectors (Ixodes ricinus) transmitting tick-borne encephalitis virus. In the Cantonal Hospital Winterthur a large number of cases are hospitalised due to endemic areas with infected ticks nearby. From 1976 until 1996 132 patients with tick-borne encephalitis were hospitalised (an average of 7 patients per year), compared with 535 cases (41 per year) in the whole of Switzerland during a similar period (1984-1992). While previously tick-borne encephalitis was considered to be a harmless illness with complete recovery, a postencephalitic syndrome after tick-borne encephalitis has recently been reported. Since the prevalence of sequelae differs in these publications, the aim of this study was to investigate sequelae in a Swiss population which had suffered from tick-borne encephalitis. We retrospectively analysed the patients with tick-borne encephalitis hospitalised in the years 1987-1996, to determine the clinical and functional outcome. A few weeks after discharge from hospital, 73% patients still had complaints, and one year later 56%. 32 patients were observed over 5 years and 31% still had some disability. After tick-borne encephalitis 10% of patients did not recover the same quality of life as before. The symptoms most frequently reported were fatigue, concentration deficits and impairment of memory. Objective neurological deficits were rare. Our results correspond well with experience in other countries and demonstrate the substantial morbidity of tick-borne encephalitis. We recommend therefore vaccination against tick-borne encephalitis, an effective measure with a low complication rate.